In the oil and gas industry, wells are drilled to target hydrocarbon bearing formations for future production. The wells are drilled using drilling mud which cools and lubricates the drilling bit, among other things. In many instances, the drilling mud includes CaCO3 or “calcite” as a weighting material to increase the density of drilling mud. This calcite can invade the hydrocarbon bearing formation during the drilling stage of the well and, after the well is put on production, the calcite will flow back inside the well and may deposit with formation rock inside the sand screens.
Hydrocarbon formations are characterized by different lithologies such as carbonate or sand stone rock formations. The sandstone formations may be unconsolidated meaning that sand production is expected once the well is put into production. Sand production has historically been problematic as it causes the erosion of down hole and surface equipment. In order to mitigate the issue of sand production in unconsolidated sandstone formations, sand screens are deployed as part of the lower well completions across the sand face.
Over time sand screens can experience accumulation of calcite, or fill. The fill negatively impacts production from the well and reduces production by restricting the flow of gas from the reservoir and plugging sand screens.
The current method for removing fill accumulations from sand screens is to deploy coiled tubing fill clean out operations. In such an operation, the Christmas tree (series of valves on top of the wellhead and known to those skilled in the art) is removed and replaced with a temporary blow out preventer to allow safe wellbore intervention. Then, a milling tool that is attached to coiled tubing and operated by a motor is run down hole and is used to drill out the fill accumulation and circulate the cuttings to surface. However, this is not a permanent solution to the problem as the fill may re-accumulate, thus requiring another deployment. Furthermore, the costly coiled tubing milling operations require shutting down the well, causing interruptions in well production. Therefore, a permanent solution is needed to prevent the accumulation of fill in sand screens.